Silicon wafer preparation for low-temperature selective epitaxial growth

Many potential selective silicon epitaxy applications demand low-temperature processing. However, the hydrogen baking that is commonly used to remove the native oxide before epitaxial deposition becomes less effective as the temperature is reduced. Therefore, making selective epitaxy manufacturable requires alternative oxide removal techniques that are reliable and noncontaminating. Exposure to the vapor over an aqueous solution of HF is investigated as a means of providing oxide-free and passivated-wafer surfaces prior to reactor loading. The dilution of the H₂O:HF mixture is found to be important in determining the oxide removal rate. An oxygen peak at the substrate interface during SIMS (secondary ion mass spectrometry) profiling is an indicator of the presence of oxide patches that can cause defects at the initiation of epitaxial deposition. Defect-free films without an interface peak of oxygen are grown at 850°C after using a 5-s exposure to the vapor over a 1:2 H₂O_:49% HF mixture followed by a 900°C hydrogen bake. A hydrogen-bake temperature of 1050°C is needed in the reactor to avoid an interfacial oxygen peak for samples not exposed to the HF vapor